1. Field of the Invention
This invention relates to design and manufacture of coil assemblies for magnetic resonance imaging.
2. Discussion of Prior Art
In designing coils, such as whole-body RF coils for creating MR images of a subject, it is highly desirable to reduce the stray RF fields produced outside of an area of interest. These stray RF fields create magnetic fields which cause interference in other electrical equipment, may induce eddy currents in nearby conductive materials, and may affect the data acquired.
One such way of reducing these fields is to use shielding, such as a passive RF shield. In MR imaging an RF transmitter coil typically has cylindrical shape encompassing a portion of the subject desired to be imaged with a Z axis passing through the length of the coil. For sake of clarification, the mathematical definition of "cylinder" will be employed throughout the remainder of the specification. This defines a cylinder to be a surface drawn by a line rotating parallel to a fixed center line and tracing out a fixed planar closed curve. This could result in a cylinder having a cross-section which is circular, elliptical, egg-shaped, or oval. The X and Y axes are orthogonal radii of the cylinder. Typically the RF shield is designed such that several coils, each which resemble a fingerprint, known as `fingerprint` coils, are disposed on the outside surface of a cylindrical body, and several are disposed on the inside surface of the cylinder body. One set has `fingerprint` coil centers which are perpendicular to an X axis through the cylinder, while the others are perpendicular to the Y axis. The magnetic flux created by these coils nulls out components of the stray fields oriented along their respective axes.
Conventional designs are constructed by disposing the coils on a flat surface and rolling such that the ends are connected. Due to the nature and geometry of the coil assembly used in shielding, half of each turn of a `fingerprint` coil, "a half-loop", is disposed near either end of the flat surface. This requires that each half-loop to be electrically connected to its other corresponding half-loop to be functional. This requires soldering, and becomes very time consuming. The connection points of the half-loops typically are not as strong as other points, and the coils may break and fail at these locations as a result of stress placed on the coil.
Currently, there is a need for constructing coil assemblies which is less time-intensive, is simpler, and results in a coil assembly having increased life and reliability.